EFFECTS OF 2 ANTIBIOTIC REGIMENS ON COURSE AND PERSISTENCE OF EXPERIMENTAL CHLAMYDIA-PNEUMONIAE TWAR PNEUMONITIS

We studied the effects of two antibiotic regimens on the course of Chl amydia pneumoniae infection in the lungs of Swiss Webster mice. After intranasal challenge with isolates AR-388 (1.3 x 10(7) inclusion-formi ng units per mouse) and AR-39 (1.5 x 10(6) inclusion-forming units per mouse), groups of animals were treated with either doxycycline (10 mg /kg of body weight once a day for 3 days), azithromycin (10 mg/kg [sin gle dose]), or saline. Responses were assessed by the isolation of org anisms in cell culture, detection of TWAR DNA in lung tissues by PCR, and lung histology. Both regimens were effective in clearing infection s induced by AR-388 (P = 0.02 and 0.007 for doxycycline and azithromyc in, respectively) compared with controls. TWAR DNA was detected in 77 and 25% of culture-negative lungs 2 weeks after treatment of AR-388 an d AR-39 infections, respectively. Histological changes showed intersti tial pneumonitis and were similar over time for all groups. Single-dos e azithromycin produced drug levels in lung tissues above the MICs for the test strains for a period three times longer than that of single- dose doxycycline. We concluded that short-term antibiotic regimens wer e successful for the treatment of experimental TWAR pneumonitis in mic e. TWAR DNA was frequently recovered from lung tissues after apparentl y successful treatment.